The 1990 Amendments to the Clean Air Act, along with a variety of related state laws, include numerous requirements related to air emissions for all types of sources. Among the methods utilized in complying with the provisions of the amended Clean Air Act is the use of scrubbers. To reduce air pollution emissions, the polluted gas is passed through a control device or system which "cleans" the gas by collecting the pollutant. Clean gas can then be safely released into the atmosphere. Scrubbers are a control device or system which effectively "clean" polluted gas prior to emission. Trexler, Kathy, THE USE OF SCRUBBERS IN CONTROLLING AIR EMISSIONS, FOCUS (a publication of Consulting Services Inc., One East Uwchlan Avenue, Suite 310, Exton, Pa., 19341), Volume 6, Issue 1, January/February 1991, page 5.
There are a number of prior art gas cleaning systems, such as those described in U.S. Pat. No. 4,949,652, to Hadley; U.S. Pat. No. 4,664,887, to Engstrom; and U.S. Pat. No. 3,700,421, to Johnson et al., each of which is incorporated herein by reference. Additionally, a prior art gas cleaning system is described in a paper presented at the Western Chapter Meeting of the American Society of Mechanical Engineers (Solid Waste Division), in Salt Lake City, Utah, on Apr. 13-14, 1988, by E. B. Mull, Jr. and Heinz P. Beutner, both of Interel Corporation, Englewood, Colo., entitled DRY ADDITIVE PROCESS FOR CONTROL OF ACID GAS AND PARTICULATE EMISSIONS, also incorporated herein by reference.
One type of scrubber is known as a fluidized bed scrubber. A fluidized bed is created by flowing a gas through a solid, such as sand. As a result of the pressurized gas flowing through the sand, the sand expands and takes on the characteristics of a fluid. Although the sand remains a dry solid, it has the characteristics of a liquid. The use of a fluidized bed is an effective of cleaning gases because the fluidized bed serves to contact pollutants which are cooled off of the gas. However, a disadvantage associated with the use of a fluidized bed scrubber is the extremely high pressure required to fluidize the bed. For example, a typical fluidized bed is 5 or 6 feet deep and requires 1.5 inches per water column (w.c.) pressure drop per inch of bed depth. Thus, a pressure loss of over 3 pounds per square inch (p.s.i.) would be required, an impractical requirement for atmospheric pressure systems.
None of the devices or systems described in the above-referenced prior art teaches the use of a fluidized bed scrubber that does not require extremely high pressures in order to fluidize the bed. Furthermore, the mechanical equipment utilized in the prior art devices or systems is sensitive to corrosion when contacted by the pollutants removed from the gases. As a result thereof, the costs associated with maintenance and/or replacement of the mechanical equipment must be taken into account in determining whether to utilize such devices or systems.
Thus, there is a need in the art for a gas cleaning system which utilizes a fluidized bed scrubber in order to effectively remove pollutants from the gas at atmospheric pressure.
There is an additional need in the art for a fluidized bed scrubber which does not require high pressures in order to sufficiently fluidize the bed.
There is an additional need in the art for a gas cleaning system which does not require frequent maintenance and/or replacement of mechanical equipment associated therewith.